1. Field of the Invention
This invention relates to heterocyclic organic compounds that may be employed as an electron donor for polymerization catalyst systems, to polymerization catalyst systems employing the heterocyclic organic compounds as an electron donor, to methods of making such polymerization catalyst systems, and to polymerization processes to produce polyolefins, particularly polypropylene, which does not contain a phthalate derivative.
2. Description of the Related Art
Ziegler-Natta catalyst systems for polyolefin polymerization are well known in the art. Commonly, these systems are composed of a solid Ziegler-Natta catalyst component and a co-catalyst component, usually an organoaluminum compound. To increase the activity and sterospecificity of the catalyst system for the polymerization of α-olefins, electron donating compounds have been widely used (1) as an internal electron donor in the solid Ziegler-Natta catalyst component and/or (2) as an external electron donor to be used in conjunction with the solid Ziegler-Natta catalyst component and the co-catalyst component.
In the utilization of Ziegler-Natta type catalysts for polymerizations involving propylene or other olefins for which isotacticity is a possibility, it may be desirable to utilize an external electron donor, which may or may not be in addition to the use of an internal electron donor. Acceptable external electron donors include organic compounds containing O, Si, N, S, and/or P. Such compounds include organic acids, organic acid esters, organic acid anhydrides, ethers, ketones, alcohols, aldehydes, silanes, amides, amines, amine oxides, thiols, various phosphorus acid esters and amides, etc. Preferred external electron donors are organosilicon compounds containing Si—O—C and/or Si—N—C bonds, having silicon as the central atom. Such compounds are described in U.S. Pat. Nos. 4,472,524; 4,473,660; 4,560,671; 4,581,342; 4,657,882; 5,106,807; 5,407,883; 5,684,173; 6,228,961; 6,362,124; 6,552,136; 6,689,849; 7,009,015; 7,244,794; 7,619,049; and 7,790,819, which are incorporated by reference herein.
Common internal electron donor compounds, incorporated in the solid Ziegler-Natta catalyst component during preparation of such component, known in the prior art, include ethers, ketones, amines, alcohols, phenols, phosphines, and silanes. It is well known in the art that polymerization activity, as well as stereoregularity, molecular weight and molecular weight distribution of the resulting polymer, depend on the molecular structure of the internal electron donor employed. Therefore, in order to improve the polymerization process and the properties of the resulting polymer, there has been an effort and desire to develop various internal electron donors. Examples of such internal electron donor compounds and their use as a component of the catalyst system are described in U.S. Pat. Nos. 4,107,414; 4,186,107; 4,226,963; 4,347,160; 4,382,019; 4,435,550; 4,465,782; 4,522,930; 4,530,912; 4,532,313; 4,560,671; 4,657,882; 5,208,302; 5,902,765; 5,948,872; 6,121,483; 6,436,864; 6,770,586; 7,022,640; 7,049,377; 7,202,314; 7,208,435; 7,223,712; 7,351,778; 7,371,802; 7,491,781; 7,544,748; 7,674,741; 7,674,943; 7,888,437; 7,888,438; 7,964,678; 8,003,558; and 8,003,559, which are incorporated by reference herein.
Most of commercial propylene polymerization catalysts currently used employ alkyl phthalate esters as an internal electron donor. However, certain environmental issues have been recently raised concerning the continued use of phthalate derivatives in human contact applications. As a result, the employment of a phthalate-free propylene polymerization catalyst is now necessary for the production of phthalate-free polypropylene to remedy these issues.
U.S. Pat. No. 7,491,781 in particular teaches the use of an internal donor in a propylene polymerization catalyst component which does not contain a phthalate derivative. However the resulted propylene polymerization catalyst has poorer hydrogen response and lower isotacticity than the catalyst containing a phthalate derivative.
The polypropylene market also has an increasing demand in high melt flow rate (MFR) grade polypropylene to reduce cycle time and to achieve down-gauging while maintaining acceptable impact strength and stiffness. High MFR polypropylene is commonly achieved by adding peroxide to the polymer, but such obtained polypropylene usually has odor issues and the physical properties are sacrificed somehow. As such, production of reactor-grade high MFR polypropylene becomes necessary to avoid these issues.
There is a continuous need for developing catalyst systems that can be used to produce polyolefins, particularly polypropylene, which does not contain a phthalate derivative. Furthermore, the desirable catalyst systems should also offer capabilities to produce polypropylene with acceptable isotacticity and high MFR.